Metal removing procedure comprises attaching a tape to a surface of a wafer, more specifically, attaching the tape to a metal on the surface of the wafer, and then separating the tape from the surface of the wafer. By this way, the unnecessary metal could be removed and the necessary metal could be retained.
There are three kinds of usual methods for removing the metal through attaching the tape on the wafer:                (1) Man-made: this method mainly comprises first attaching the tape to the surface of the wafer, and then repeatedly pressing the tape to adhere the tape to the metal on the surface of the wafer, and finally separating the tape from the wafer. Therefore, the unnecessary metal could be separated from the wafer and transferred to the tape, and the necessary metal could be retained. However, it must repeatedly press the tape to fully adhere the tape to the metal on the surface of the wafer. Meanwhile, a force is also applied to the metal or the photo-resistor so the metal or the photo-resistor is prone to deform and the wafer yield would be decreased. Furthermore, it is hard to control every forces applying to the tape each time. The tape might not fully adhere to the surface of the wafer, hence the unnecessary metal would not be fully removed and the wafer yield may drop.        (2) Machine: this method mainly comprises adhering the tape to the surface of the wafer by a fixture, and then the fixture repeatedly pressing the tape to adhere the tape to the metal on the surface of the wafer, and finally a machine driving the tape to tear the tape from the wafer. The unnecessary metal is transferred to the tape and separated from the wafer, and the necessary metal is retained. However, since the wafer is prone to warp in the process, the pressure repeatedly applied by the fixture on the tape will cause the wafer to break. Moreover, there are concave-convex positions on the surface of the wafer, and the fixture has difficulty to press those concave-convex positions. Therefore, the adhesive ability between the metal and the tape is weak, and it would decrease the wafer yield since the unnecessary metal could not be fully removed.        (3) Chemical solutions: this method comprises soaking the wafer in the chemical solution to loosen the photo-resistor on the surface of the wafer (this step could be omitted depending on the technique). Then, spreading two pressurized fluids (water and air) or three pressurized fluids (water, air and steam) on the surface of the wafer in order to expel the photo-resistor and the unnecessary metal thereon away from the surface of the wafer and retain the necessary metal. However, when the temperature of the chemical solutions changes violently, the wafer will break. After the chemical solutions spread on the surface of the wafer, the electrical properties of the wafer are likely to be abnormal since the static electricity occurred then. Moreover, the removed metal is prone to scrap the surface of the wafer when being driven by the chemical solutions.        